There is a treatment method that is becoming popular, which is for recovering an oral function that has been lost at a defective tooth part. This treatment method uses a dental implant system for fixing a dental prosthesis on the oral cavity inner side of a dental implant fixture that is embedded into the jawbone at the defective tooth part to act as an artificial dental root that is directly connected to the jawbone. This dental implant system typically has a structure in which a dental abutment, which pierces through the gum, is arranged on the oral cavity inner side of the dental implant fixture, and the dental prosthesis is arranged on the oral cavity inner side of this dental abutment.
The gum tissue after a tooth is extracted at the part that is treated by using the above dental implant system, has a feature of having less fibroblast cells compared to that of the gum before the tooth is extracted. Thus, germs can easily enter the jawbone from between the periphery of the dental abutment and the gum. Furthermore, the ability of restoring the tissue that has been destroyed by inflammation is low, which tends to be the factor of causing bone absorption to proceed.
Furthermore, the gum tissue (collagen tissue) in the gum before extracting the tooth is reproduced so as to be orthogonal with respect to the natural tooth. Meanwhile, in the tissue that is reproduced after embedding the dental implant fixture, the gum tissue is reproduced so as to be parallel to the dental implant fixture. The gum tissue parallel to the dental implant fixture is weakly combined with the contacting dental implant fixture and the contacting dental abutment, and therefore gum recession is likely to occur.
When the gum recession occurs as described above, the leading end side of the gum contacting the dental abutment recedes, and germs enter into the jawbone, which often causes bone absorption and reduces the sensuousness. As a measure for such a problem, there is a transmucosal element (dental abutment or spacer), which is provided with a groove or a recessed part that extends entirely or partially around its periphery, in order to integrate the gum and the transmucosal element (see, for example, Patent Document 1, claim 8). This groove is formed to increase the stability of the surrounding gum. However, as described above, the gum tissue after extracting the tooth has a different scar tissue from that of the gum tissue before extracting the tooth. Therefore, even if an attempt is made to integrate the gum and the transmucosal element by providing a groove, it is difficult to achieve the same effects as those of the gum tissue before extracting the tooth.
As a countermeasure for the problem of the difficulty in preventing the gum recession as described above, there is a method of fabricating a new dental abutment having a rim part that can cover the gap formed between the gum and the dental abutment, directly using the dental implant fixture that is already embedded in the jawbone, and newly applying this new dental abutment and the dental prosthesis thereof. This method is the most practical countermeasure because the sensuousness is not reduced and the procession of bone absorption can be delayed.
Generally, as a dental abutment, there is a type having a ready-made form prepared by each implant manufacturer, and there is a type that is fabricated from a dental block prepared in advance, by a device that is mechanized/automated by a CAD/CAM system. An example of a frequently used dental block has a substantially rectangular parallelepiped shape, in which an engagement portion for engaging with a dental implant fixture that is commonly required for dental abutments that have been cut into any shape, and a bolt through hole for inserting a bolt that is required for engaging the dental abutment with the dental implant fixture, are formed in advance.
However, before the gum recedes, the surface where the dental abutment abuts against the gum has a shape that is warped up toward the oral cavity inner side (FIG. 8); however, after the gum has receded, the surface where the dental abutment abuts against the gum has a shape that is directed downward toward the residual ridge side (FIG. 6). Therefore, it is difficult to fabricate a dental abutment for before gum recession and a dental abutment for after gum recession, from dental blocks having the same shape.
That is to say, as for a dental abutment before gum recession, it is easy to fabricate a dental abutment in which the surface that abuts against the gum has a shape that is warped up toward the oral cavity inner side, by using a dental block in which the engagement portion which engages with the dental implant fixture is provided in a protruding condition in advance, and simply cutting the part near the engagement portion, for example as illustrated in FIG. 7. However, by a dental block as illustrated in FIG. 7, it is not possible to perform a cutting process from the part near the engagement portion which engages with the dental implant fixture, such that the part to cover the part where the gum has receded, is in a protruding condition. Therefore, unless a significant process is performed, such as processing the entire dental block again including the engagement portion which engages with the dental implant fixture, it is not possible to form a dental abutment for after gum recession by cutting a conventional dental block as described above.